1. Field of the Invention
The present invention relates to controlling a fuel injection of a diesel engine equipped with a fuel injection device performing a multistage injection.
2. Related Art
As a fuel injection system of a diesel engine, there is well-known a common-rail (electronically-controlled accumulator) system.
Because the common-rail can store a high-pressure fuel into a vessel called a rail, it has a feature capable of adjusting an injection pressure of the fuel so as to inject it, regardless of an engine rotation speed or a load. The common-rail can also inject an optimal amount of fuel at an optimal timing using an electronic control. Therefore, the diesel engine can freely inject the fuel using the electronic control and the common-rail system. Thus, the performance of the diesel engine, such as an output, a fuel consumption and an exhaust gas, has been remarkably improved, due to the common-rail system.
When the common-rail injects the fuel by compressing an intake air, it can inject the fuel by multistage injections (a multistage injection control). In general, each of the injections is referred to as a pilot injection, a pre-injection, a main injection, an after injection, a post injection or the like, in order of earlier injection timing. For example, the pilot injection injects the fuel prior to the main injection so as to mix the air and the fuel before igniting, thereby reducing a combustion sound peculiar to the diesel engine.
In the multistage injection control of the common-rail, for example, there are well-known some improvements in the pilot injection. JP 1998-122022 discloses a fuel injection device that stops the pilot injection while a surging is generating. JP 2000-205021 discloses a fuel injection device that stops the pilot injection when a main injection quantity is larger than a pilot injection quantity.    Patent Literature 1: the Japanese Patent Laid Open Gazette 1998-122022    Patent Literature 2: the Japanese Patent Laid Open Gazette 2000-205021
In recent years, a problem of smoke discharged from the exhaust gas of automobiles has become an environmental nightmare. Smoke generally include white smoke, blue smoke and black smoke. Herein, white smoke is defined as white smoke discharged at an engine starting or soon after starting. A sprayed fuel collides with a combustion chamber wall surface at low temperature so as to attach to it, and the attached fuel is combusted and discharged without enough evaporation, whereby white smoke is generated. Therefore, the generation of white smoke is improved by reducing the amount of fuel attached to the combustion chamber wall surface.
Using the common-rail electronic control injection device, required fuel can be divided and injected into a cylinder by multistage injections. Consequently, since injection quantity and injection time per injection are reduced, a penetrating power of fuel injection is weakened, and at the same time, the amount of fuel attached to the wall surface is decreased. Therefore, as the number of injections is increased, the discharging efficiency of white smoke is improved.